libstdc++-v3/src/hash.cc

//  std::hash and std::tr1::hash definitions -*- C++ -*-

// Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

#include <cstddef>
#include <string>
#include <cmath>

#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <functional>
#  define _GLIBCXX_BEGIN_NAMESPACE_TR1 
#  define _GLIBCXX_END_NAMESPACE_TR1 
#else
#include <tr1/functional>
#  define _GLIBCXX_BEGIN_NAMESPACE_TR1 namespace tr1 {
#  define _GLIBCXX_END_NAMESPACE_TR1 }
#endif

namespace std
{
_GLIBCXX_BEGIN_NAMESPACE_TR1

  // For long double, careful with random padding bits (e.g., on x86,
  // 10 bytes -> 12 bytes) and resort to frexp.
  template<>
    size_t
    hash<long double>::operator()(long double __val) const
    {
      size_t __result = 0;

      int __exponent;
      __val = std::frexp(__val, &__exponent);
      __val = __val < 0.0l ? -(__val + 0.5l) : __val;

      const long double __mult =
      __gnu_cxx::__numeric_traits<size_t>::__max + 1.0l;
      __val *= __mult;

      // Try to use all the bits of the mantissa (really necessary only
      // on 32-bit targets, at least for 80-bit floating point formats).
      const size_t __hibits = (size_t)__val;
      __val = (__val - (long double)__hibits) * __mult;

      const size_t __coeff =
	__gnu_cxx::__numeric_traits<size_t>::__max / __LDBL_MAX_EXP__;

      __result = __hibits + (size_t)__val + __coeff * __exponent;

      return __result;
    };

#ifndef _GLIBCXX_LONG_DOUBLE_COMPAT_IMPL
  template<>
    size_t
    hash<string>::operator()(string __s) const
    { return _Fnv_hash<>::hash(__s.data(), __s.length()); }

  template<>
    size_t
    hash<const string&>::operator()(const string& __s) const
    { return _Fnv_hash<>::hash(__s.data(), __s.length()); }

#ifdef _GLIBCXX_USE_WCHAR_T
  template<>
    size_t
    hash<wstring>::operator()(wstring __s) const
    {
      const char* __p = reinterpret_cast<const char*>(__s.data());
      return _Fnv_hash<>::hash(__p, __s.length() * sizeof(wchar_t));
    }

  template<>
    size_t
    hash<const wstring&>::operator()(const wstring& __s) const
    {
      const char* __p = reinterpret_cast<const char*>(__s.data());
      return _Fnv_hash<>::hash(__p, __s.length() * sizeof(wchar_t));
    }
#endif
#endif

_GLIBCXX_END_NAMESPACE_TR1
}